The acetylene-terminated polyphenylquinoxalines, disclosed in U.S. Pat. No. 3,966,729, are one of the most promising new matrix resins for advanced aircraft and aerospace systems. The materials propagate and cure by addition reactions to form high molecular weight, thermally stable compositions. The addition process obviates all problems associated with volatile by-product formation that occurs when such materials are prepared by the normal condensation process. The new resins demonstrate an excellent potential for use as matrices in high performance structural composites.
The principal drawback in the acetylene-terminated quinoxaline system disclosed in the aforementioned patent is the difficulty in working with the very unstable 4-(3-ethynylphenoxy)orthophenylene diamine utilized as the oligomer endcapping agent. Because of the susceptibility of the endcapping agent to oxidation, it cannot be isolated and stored for any length of time. As a result, the resins prepared with the agent are very costly, an important factor in selecting resins for use as composite matrices.
It is a principal object of this invention, therefore, to provide improved acetylene-containing endcapping agents that overcome the shortcomings of the agent disclosed in the aforementioned patent.
Another object of the invention is to provide a process for preparing the acetylene-containing endcapping agents.
A further object of the invention is to provide improved acetylene-terminated phenylquinoxaline oligomers which exhibit low softening points, thereby making such materials more amenable to composite fabrication.
Still another object of the invention is to provide a process for preparing the acetylene-terminated phenylquinoxaline oligomers.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the ensuing disclosure.